FRS stocks Hebel blocks. Hebel’s advanced technology results in a versatile light weight fire resistant block allowing for easy installation. It also provides for a high insulation and acoustic value plus can be cut with a hand saw and provides up to 4 hours fire protection.

I tried Hebel, but it was only 1" thick and it cracked from the heat after a month or so. Might be ok if it's thicker but it is made from Portland cement. Glass stumpers use it for moulds when they fire the glass ( to around 900 C) after several firings it needs to be replaced. The insulating fire bricks will last better as they can handle the heat and have better thermal shock resistance.

I might be wrong but I thought that there was a insulating firebrick that you can not cut with a hand saw therefore eliminating the health issue. This is the kind of brick that I was thinking (if it exists). I seem to recall being warned about what kind I need to buy.

Hebel as an insulating door is great there is not enough heat in a cooling oven to effect it. I have had the same temp. door for over a year before rebuilding another again from hebel. I have also built one for a friend which works well. I have changed my original design and do not bolt them together but us silastic to glue the hebel to a piece of wood. Yes the downside is they are brittle and you can chip the edges quite easily. But there cheap to replace and easy to make all you need is a handsaw and rasp to cut and form it to fit your reveal. I have not used insulating fire brick before but they posibly be alittle tougher than hebel but I recon you could make the same type of door using silastic to glue to the wood. And perhaps have to use power tools to shape. I would consider the weight factor as well we all tend to overmake things sometime and it could become to heavy to use if made to thick.

I just used a masonary type rated to 200C no probs to date
I used 3'' to start with but found it to heavy so I sawed it down to 2" the doors is 500mmx350mm (20"x14") which weighs in a a bit under 9 kg ( sorry can't convert this in my head)

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